<meta charset="utf-8">
(#) Frequently changing state should not  be directly read in composable function

!!! WARNING: Frequently changing state should not  be directly read in composable function
   This is a warning.

Id
:   `FrequentlyChangedStateReadInComposition`
Summary
:   Frequently changing state should not  be directly read in composable function
Severity
:   Warning
Category
:   Performance
Platform
:   Any
Vendor
:   Jetpack Compose
Identifier
:   androidx.compose.foundation
Feedback
:   https://issuetracker.google.com/issues/new?component=612128
Min
:   Lint 8.0 and 8.1
Compiled
:   Lint 8.7+
Artifact
:   [androidx.compose.foundation:foundation-android](androidx_compose_foundation_foundation-android.md.html)
Since
:   1.5.0
Affects
:   Kotlin and Java files and test sources
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/main/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetector.kt)
Tests
:   [Source Code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/test/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetectorTest.kt)
Copyright Year
:   2022

This property is observable and is updated after every scroll or
remeasure. If you use it in the composable function directly, it will be
recomposed on every change, causing potential performance issues
including infinity recomposition loops. Prefer wrapping it with
derivedStateOf to use calculation based on this property in composition
or collect changes inside LaunchedEffect instead.

!!! Tip
   This lint check has an associated quickfix available in the IDE.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/androidx/compose/foundation/foo/test.kt:10:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val index = state.firstVisibleItemIndex
                ---------------------------
src/androidx/compose/foundation/foo/test.kt:11:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val offset = state.firstVisibleItemScrollOffset
                 ----------------------------------
src/androidx/compose/foundation/foo/test.kt:12:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val layoutInfo = state.layoutInfo
                     ----------------
src/androidx/compose/foundation/foo/test.kt:17:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val index = state.firstVisibleItemIndex
                ---------------------------
src/androidx/compose/foundation/foo/test.kt:18:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val offset = state.firstVisibleItemScrollOffset
                 ----------------------------------
src/androidx/compose/foundation/foo/test.kt:19:Warning: Frequently
changing state should not be directly read in composable function
[FrequentlyChangedStateReadInComposition]
    val layoutInfo = state.layoutInfo
                     ----------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/androidx/compose/foundation/foo/test.kt`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~kotlin linenumbers
package androidx.compose.foundation.foo

import androidx.compose.runtime.Composable
import androidx.compose.foundation.lazy.grid.LazyGridState
import androidx.compose.foundation.lazy.LazyListState

@Composable
fun TestGrid(state: LazyGridState) {
    val index = state.firstVisibleItemIndex
    val offset = state.firstVisibleItemScrollOffset
    val layoutInfo = state.layoutInfo
}

@Composable
fun TestList(state: LazyListState) {
    val index = state.firstVisibleItemIndex
    val offset = state.firstVisibleItemScrollOffset
    val layoutInfo = state.layoutInfo
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/androidx/platform/frameworks/support/+/androidx-main:/compose/foundation/foundation-lint/src/test/java/androidx/compose/foundation/lint/LazyLayoutStateReadInCompositionDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `LazyLayoutStateReadInCompositionDetector.observablePropertiesUsedInComposableFunction`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=612128.

(##) Including

!!!
   This is not a built-in check. To include it, add the below dependency
   to your project.

```
// build.gradle.kts
implementation("androidx.compose.foundation:foundation-android:1.8.0-alpha07")

// build.gradle
implementation 'androidx.compose.foundation:foundation-android:1.8.0-alpha07'

// build.gradle.kts with version catalogs:
implementation(libs.foundation.android)

# libs.versions.toml
[versions]
foundation-android = "1.8.0-alpha07"
[libraries]
# For clarity and text wrapping purposes the following declaration is
# shown split up across lines, but in TOML it needs to be on a single
# line (see https://github.com/toml-lang/toml/issues/516) so adjust
# when pasting into libs.versions.toml:
foundation-android = {
    module = "androidx.compose.foundation:foundation-android",
    version.ref = "foundation-android"
}
```

1.8.0-alpha07 is the version this documentation was generated from;
there may be newer versions available.

NOTE: These lint checks are **also** made available separate from the main library.
You can also use `androidx.compose.foundation:foundation-lint:1.8.0-alpha07`.


[Additional details about androidx.compose.foundation:foundation-android](androidx_compose_foundation_foundation-android.md.html).
(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("FrequentlyChangedStateReadInComposition")
  fun method() {
     problematicStatement()
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("FrequentlyChangedStateReadInComposition")
  void method() {
     problematicStatement();
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection FrequentlyChangedStateReadInComposition
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="FrequentlyChangedStateReadInComposition" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'FrequentlyChangedStateReadInComposition'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore FrequentlyChangedStateReadInComposition ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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